Automatic dryer control circuit



May 3, 1966 J. c. WORST AUTOMATIC DRYER CONTROL CIRCUIT 2 Sheets-Sheet 1 Filed March 25, 1964 INVENTOR. JOSEPH c. woes-r BY ms ATTORNEY y 1966 J. c. WORST 3,248,799

AUTOMATIC DRYER CONTROL CIRCUIT Filed March 25, 1964 2 Sheets-Sheet 2 I00 I 96 I03 104- AR I I I as L LJ J I- 34 INVENTOR.

TOSEPH c, wmzsr MWW H4 5 A oRMEY 3 w I I -g United States Patent 3,248,799 AUTOMATIC DRYER CONTROL CIRCUIT Joseph C. Worst, Louisville, Ky., assignor to General Electric Company, a corporation of New York Filed Mar. 25, 1964, Ser. No. 354,689 9 Claims. (Cl. 34-45) This invention relates to domestic fabric drying machines, and more particularly to an electrical control system for use in such machines.

There are many types of dryer control circuits which provide for terminating operation of the dryer when it is sensed that the fabics within the dryer have achieved a predetermined degree of dryness. There are a variety of such circuits; the basis for determining dryness may be made to be a temperature function, or an air humidity function, for instance. Another approach with su'bstanial reliability is to actually sense to what extent the fabrics themselves are electrically conductive, since fabrics normally present a high electrical resistance, and it is only when they have a substatnial amount of moisture in them that their resistance decreases appreciably.

Accordingly, there are on the market some domestic fabric dryers in which this approach is taken, that is, the conductivity of the fabrics is used to determine when the drying operation will be ended, or when steps will be taken to initiate ending of the operation. Heretofore, it has been deemed necessary to integrate the sensing over a period of time. This was felt important because, in domestic fabric dryers, the fabrics are tumbled during drying and at any given instant they may be out of contact with the sensing element. Thus, it was deemed important to preclude the machine from determining that dryness has been achieved simply because there is a brief period when a high resistance appears across the sensing elements. This limitation on machines which sense the conductivity of the fabrics in order to determine dryness has required the incorporation of relatively expensive components.

In the concurrently filed application Serial No. 354,490, filed March 25, 1964, of Earl F. Pierce, Jr., there is described and claimed an invention based on the concept of stopping the advance of a sequence control mechanism toward termination of operation whenever the resistance sensed is low, that is, whenever wet clothes are sensed, and causing such advance at other times. This has substantially eliminated the requirement for expensive components (such as are provided in present machines) which nonetheless do not completely eliminate the possibility of an erroneous triggering of the end of the operation. My invention is an improvement over the invention of the Pierce application, which invention was made by said Pierce prior to my invention. I, therefore, do not claim herein anything shown or described in said Pierce application, which is to be regarded as prior art with respect to the present application.

It is an object of my invention to provide a dryer control circuit wherein the conductivity of the fabrics is used as the criterion for termination of the operation, but wherein there is no need to integrate the sensing results over a period of time.

More specifically, it is an object of my invention to achieve this goal by causing the sensing elements to control directly the operation of a timer mechanism, so that the timer runs whenever the sensing elements have a high resistance across them regardless of the point at which it occurs in the cycle.

Yet more specifically, it is an object of my invention to achieve the desired goal by providing a shunt across an electrically operated timer mechanism, with the shunt being controlled by the sensing element so that it is effective to provide the shunting function and prevent operation of the timer mechanism when the clothes are wet, but ceases to be effective to act as a shunt and therefore provides operation of the timer mechanism when the clothes become dry.

In carrying out my invention in one form thereof, I provide a fabric drying machine which has the conventional chamber for receiving fabrics to be dried, together with drying means arranged to cause evaporation of moisture from fabrics placed in the chamber. Together with this there is provided means for tumbling fabrics in the chamber. Spaced conductors are positioned so as to be bridged by the tumbling fabrics so that the conductors are provided with a relatively low resistance electrical bridge when there is substantial moisture in the fabrics which bridge the conductors.

Together with this structure I provide sequence control means; this may, for instance, include a conventional timer motor operating a cam through a gear reduction assembly effective, after a predetermined length of its operation, to terminate operation of the drying means. The sequence control means is controlled by the spaced conductors so that operation of the sequence control means is precluded whenever the conductors have a relatively low resistance electric-a1 bridge across them, and is enabled at other times.

-It has been found that, by so relating the sequence control means to the bridging of the spaced conductors, proper drying is readily achieved without the need for integrating the sensing function over a period of time. Preferably, a suitable shunting device, such as a silicon controlled rectifier, connected across electrically operated sequence control means, is made conductive when the resistance across the spaced conductors is low. As a result, the electrical sequence control mechanism is shunted out of the circuit.

The subject matter which I regard as my invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. My invention, however, both as to organization and method of operation together with further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a side elevational view of a clothes dryer incorporating my improved dryer control arrangement, the view being partly broken away and partly broken away and partly sectionalized in order to illustrate details;

FIGURE 2 is a schematic illustration of my improved control system as used in the control of the drying machine of FIGURE 1; and

FIGURE 3 is a second embodiment of my invention as it may be applied to the drying machine of FIGURE 1.

Referring now to FIGURE 1, the machine illustrated is a domestic clothes dryer, generally indicated by the numeral 1. Dryer 1 is provided in the usual way with a cabinet 2 having a front door 3 to provide access to the interior of the cabinet for loading or unloading clothes. Provided on the top wall 4 of cabinet 2 is a control panel 5 which may include a suitable manual control 6 connected to a sequence control assembly 7. By manual setting of control 6, the machine may be caused to start and, as will be explained below, automatically proceed through a cycle of operation.

Within cabinet 2, there is provided a clothes tumbling container, or drum, 8 which constitutes a chamber for receiving fabrics to be dried and which is mounted for rotation on a substantially horizontal axis. Drum 8 is substantially cylindrical in shape, having a first cylindrical outer wall portion 9, second and third outer cylindrical wall portions and 11 located respectively adjacent the front and back of the drum, a front wall 12, and a back wall 13. Outer wall portions 9, 10 and 11 are imperforate over their entire length, so that the entire outer shell of the basket is imperforate. On the interior surface of central portion 9 there is provided a plurality of clothes tumbling ribs 14 formed of a suitable heat-resistant insulating material. Over each rib extend a number of conductors or wires 15 and 16, spaced from each other and which alternate with each other along the length of the rib. The purpose of these wires, and the structure to which they are related, will be more fully discussed herebelow.

The front of drum 8 may be rotatably supported within outer casing 2 by suitable idler wheels, one of which is shown by the numeral 17. These wheels are rotatably secured to the top of a member 18 which extends up from base 19 of the machine. Wheels 17 are disposed beneath the drum in contact with portion 10 on each side to provide a stable support.

The rear end of drum 8 receives its support by means of a stub shaft 20 extending from the center of wall 13. Shaft 20 is secured within a bearing 21 formed in a baflie 22 which in turn is rigidly secured to the back wall 23 of cabinet 2 by any suitable means such as, for instance, welding at a number of points 24. With the arrangement shown, the basket may rotate on a horizontal axis, with wheels 17 providing the front support and stub shaft 20 within bearing 21 providing the rear support.

It is to be noted at this point that stub shaft 20 is provided with a central opening 25. The wires 15 and 16 all extend from ribs 14 around the back of drum 8 and down through suitable openings in a baffle member 26; the wires then extend through the opening formed through shaft 20. At the outer end of shaft 20, a disc 27 may be formed as shown with the conductors 15 being secured to a conductive outer ring portion 28 and the conductors 16 being secured to a conductive inner ring portion 29. Portions 28 and 29 are electrically insulated from each other; this may readily be done by making disc 27 of an insulating material, with the ring portions embedded therein. A contact member 30 is continually in contact with conductor portion 28 while, similarly, a conductor member 31 is continuously in contact with conductive portion 29 of the disc. Thus, all of the conductors 15 are connected to stationary conductor 30 and all of the conductors 16 are similarly connected through similar means to stationary conductor 31.

In order to provide for the flow of a stream of drying air through the clothes drum, the drum is provided with a central aperture 32 in its front wall 12 and with an opening in the form of a plurality of perforations 33 in its rear wall 13, the perforations in the present case being formed to extend around the rear wall in an annulus.

As has been stated, bafile member 22 is rigidly secured to rear wall 23 of cabinet 2. Baffle member 22 also serves to support suitable heat drying means such as electrical heating elements 34 appropriately insulated from bafiie member 22. Elements 34 may be annular in shape so as to be generally coextensive with perforations 33 in drum 8. As previously mentioned, the other baffle member 26 is rigidly secured to the back wall 13 of the drum outside the ring of perforations 33 and within stationary baffle 22, so that an annular air inlet 35 is in effect formed by baffles 22 and 26. In this manner, a passage is formed for air to enter annular inlet opening 35 between the baffles pass over the heater 34, and then pass through openings 36 formed in baflie 26 to the interior of drum 8.

The front opening 32 of the drum is substantially closed by means of a stationary bulkhead generally indicated by the numeral 37. Bulkhead 37 is made up of a number of adjacent members including the inner surface 38 of access door 3, a stationary frame 39 for the door formed as a flange of the front wall 40 of the cabinet, the inner surface member 41 of an exhaust duct 42 which is formed by the cooperation of member 41 with the front wall 40 of the cabinet, and an annular flange 43 mounted on frame 39 and on the duct wall. It will be noted that a suitable clearance is provided between the inner edge of the drum opening 32 and the edge of bulkhead 37 so that there is no rubbing between the drum and bulkhead during rotation of the drum. In order to prevent any substantial air leakage through opening 32 between the interior and exterior of the drum, a suitable ring seal 44, preferably formed of felt-like material, is secured to flange 43 in sealing relationship with the exterior surface of drum wall 12.

Front opening 32, in addition to serving as part of the air flow path through the drum, also serves as a means whereby clothes may be loaded into and unloaded from the drum. Door 3, whose inner surface forms part of the bulkhead closing the opening, is mounted on cabinet 2 so that when the door is opened clothes may be inserted into or removed from the drum through the door frame 39. It will be noted that the door includes an outer flat imperforate section 45 and an inwardly extending hollow section 46 mounted on the flat outer section. Hollow section 46 extends into the door frame 39 when the door is closed, and the door surface 38 which comprises part of the combination bulkhead 37 is actually the inner wall of the hollow section.

The air outlet from the drum is provided by a perforated opening 47 formed in the inner wall 38 of hollow door section 46. The bottom wall section of door 3 and the adjacent wall of door frame 39 are provided with aligned openings 48 and 49, opening 49 providing the entrance to duct 42. As shown, a lint trap 50, which may comprise a fine mesh bag, is preferably positioned across duct 42 at opening 49, the bag being supported by the door frame 39. Duct 42 leads downwardly to an opening 51 formed in member 18 which supports wheels 17. Opening 51 constitutes the inlet to a blower member 52 contained within a housing 53 and directly driven by an electric motor 54. The blower draws ambient air in through any appropriate opening in the cabinet such as, for instance, through opening 55. From opening 55 the air is drawn over heaters 34, then through the basket, then through door 3 and duct 42, and into blower 52. From the blower the air passes through any appropriate duct (not shown) out of cabinet 2 so as to be exhausted from the machine.

In addition to driving blower 52, motor 54 constitutes the means for effecting rotation of drum 8. In order to effect this, motor 54 is provided with a shaft 56 having a small pulley 57 formed at the end thereof. A belt 58 extends around pulley 57 and also entirely around the cylindrical wall section 9 of drum 8. The relative circumferences of pulley 57 and wall section 9 cause the drum to be driven by the motor at a speed suitable to effect tumbling of the clothes therein. In order to effect proper tensioning of belt 58 there may be provided a suitable idler assembly 59 secured on the same support 60 which secures one end of the motor.

Thus, the air is pulled through the drum and at the same time the fabrics in the drum are tumbled. When the air is heated by heating elements 34, the heated air passing through the drum causes vaporization of moisture from the clothes. The vapor is carried off with the air as it passes out of the machine.

The operation of dryer 1 is controlled by the new and improved control system shown in the circuit diagram of FIGURE 2. As shown therein, the entire control system of the machine may be energized across a 3-wire power supply system Which includes supply conductors 61 and 62 and a neutral conductor 63. For domestic use, conductors 61 and 62 will normally be connected across a 220 volt power supply, with volts appearing between the neutral line 63 and each of the conductors and with the neutral line being at ground voltage. Motor 54, connected between conductors 61 and 63, is a singlephase induction-type motor having a main winding 64 and a start winding 65 both connected at a common end to a conductor 66 through a conventional door switch 67 (which is closed when door 3 is closed and is opened when the door is open). Conductor 66 is connected to conductor 63.

Start winding 65 is connected in parallel with main winding 64 under the control of a speed responsive device, such as that shown at 68, which is schematically shown as connected to the rotor 69 of the motor. The speed responsive device 68 controls a switch 70 which is engageable with either a contact 71 or a contact 72, being engaged with contact 71 when the motor is at rest and moving into engagement with contact 72 as the motor comes up to speed. It can readily be seen that engagement with contact 71 connects start winding 65 in parallel with main Winding 64, while movement of switch 70 away from this position opens the start winding. Thus, as rotor 69 comes up to speed the start winding becomes de-energized and the motor then continues to run on main winding 64 alone.

The starting of the motor is provided by an manually operable switch 73 which may, for instance, in the structure of FIGURE 1, be moved to its closed position by pulling out on member 6. Switch 73 connects the motor to supply conductor 61 through contacts 74 and 75 of a switch 76 which also includes a third contact 77. Switch 73 is normally biased to the open position shown. However, when member 6 is pulled out manually, and provided switch 76 is closed, energization of the motor is provided. Within less than a second then, under normal circumstances, the motor comes up to speed so that switch 7 engages contact 72. As a result of this movement of switch 7, the main winding 64 of motor 54 continues to be energized by the bypass around switch 73 when member 6 is released and switch 73 opens.

A conventional timer motor assembly 78 may be provided in order to control a cam 79 which in turn controls the switch 76; the timer motor, cam and switch provide together a conventional sequence control mechanism. Cam 79 is also movable by rotation of member 6 in the usual way, so that when operation of the machine is desired member 6 may be rotated until came 79 causes switch 76 to close all three of its contacts. The machine operation is terminated, as will be seen herebelow, when cam 79 has been rotated sufficiently by timer motor 78 to open the contacts of switch 76.

An energizing circuit is also completed for heater 34 through the following circuit. Starting at conductor 6-1, the circuit proceeds through contacts 75 and 77 of switch 76, and then through a conductor 80 to a conventional temperature-controlling thermostat 81 of the type which is frequently provided in connection with fabric drying machines of the type shown. From thermostat 81, the circuit proceeds through heater 34 and a conventional safety thermostat 82 to a conductor 83 leading back to conductor 62 through a switch 84 Switch 84 is controlled by centrifugal member 68, being closed only when the motor has come up to speed so that there can be no energization of heater 34 except when motor 54 is operating properly.

The operation of timer motor 78 is effected by energizing the timer motor through a circuit which, starting at conductor 61, proceeds through contacts 75 and 74 of switch 76, then to the timer motor 78, and then through a resistor 85 back to conductor 63. A shunt across the timer motor 78 is provided, and in this case I have shown the shunting being achieved by a silicon controlled rectifier 86 which is, as shown, connected directly across the timer motor. Rectifier 86 includes a gate 87; in the conventional manner, when a sufficient voltage is impressed at the gate of the rectifier the rectifier becomes conductive for one direction of current flow.

Generally, conventional timer motors which are commercially used are not operative when they receive only half of each cycle of 60 cycle alternating current; thus, shunting of the timer motor for half of each alternating current cycle will effectively stop the operation of timer motor 78.

The voltage impressed at gate 87 of rectifier 86 is deter mined through a circuit which includes a suitable resistor 88, conductors 15 and 16, and a conventional rectifier 89. It will be clear that when the fabrics are quite wet, then during the period that they bridge conductors 15 and 16 they will permit a sufliciently high voltage to be impressed at gate 87 for rectifier 86 to be conductive. As a result, at such times the timer motor will not cause rotation of cam 79. However, any time that the resistance across conductors 15 and 16 rises to the extent that the gate voltage of rectifier 86 is not sufficient to cause it to become conductive, the timer motor does operate.

There will be brief intervals even early in a drying operation when, due to the tumbling action, the resistance across the elements 15 and 16 will briefly be quite high because none of the fabrics are properly bridging them. The timer motor will therefore run, but only briefly since, for a very substantial proportion of the time when the fabrics are wet, they will be bridging conductors 15 and 16.

As the clothes start to become dry, the periods when the resistance across conductors 15 and 16 is too high to permit conducting by rectifier 86 will become more frequent and longer, and the timer motor will run more. For instance, if some of the clothes dry more quickly than others, they will act as a high resistance when they are across conductors 15 and 16, whereas the other clothes which are still in a wetter state will permit a suflicient gate voltage for rectifier 86 to conduct. Thus, as the clothes become drier, the proportion of the time that the timer motor runs increases. Toward the end of a cycle, the timer motor will run almost continuously, and will quickly toll out the cycle, rotating the cam 79 to the point at which switch 76 opens to the position shown.

It has been found that this provides a highly effective drying cycle, where the conductivity of the clothes is used as the dryness measurement yet Where the need for integrating this conductivity over a period of time is eliminated without any loss of effectiveness.

There is shown in FIGURE 3 a second embodiment of a control circuit conforming to my invention wherein parts which are identical to those shown in FIG- URE 2 will be referred to by the same numerals: It will be understood that the motor structure and circuitry, the timer motor, and its control of the cam and switch and the heater circuit, are all like these structures and their functions in FIGURE 2.

In this case, the primary winding 90 of an isolation transformer schematically indicated at 91 (which may, for instance, be a step-down transformer) is connected in parallel with motor 54. Transformer 91 further includes, in the conventional manner, a core 92 and a secondary winding 93. The secondary winding 93 is connected so as to be able to energize the timer motor 78 through a circuit which includes a resistor 94.

As opposed to the two sets of spaced conductors 15 and 16 of FIGURE 2, there are shown in FIGURE 3 three sets of spaced conductors 95, 96 and 97. Conductors 97 are connected to one side of the transformer secondary 93 through a half wave rectifier 98, and similarly the conductors 96 are connected to the other side of the secondary 93 through a half wave rectifier 99. This means that when a suitable bridge exists between either or both of the conductors 96 and 97, and the conductor 95, a direct current will be impressed at the gates 100 and 101 of a pair of silicon controlled rectifiers 102 and 103. These gates are connected to the conductors through a suitable resistor 104.

Rectifier 102 provides a shunt across timer motor 78 for one direction of alternating current generated in secondary winding 93, and rectifier 103 provides a shunt across the timer motor for the other half cycle of the alternating current cycle. It will thus be seen that the net result is to provide a complete shunting of the timer motor 78 when a suitable bridging is provided by wet tumbling fabrics. It will be seen that the timer, the sensing conductors, and the complete dryer control system, are on the low voltage side of the step-down transformer 91, thereby making possible the use of lower cost devices and isolating all parts of the control system from the power line. It will be observed that these results are achieved again in a circuit wherein no time integration of the conductivity of the fabrics is required, but where there is an immediate response to a high resistance across the sensing conductors by operation of the timer motor, this operation of the timer motor ceasing as soon as a low resistance bridge is re-established, just as was described in connection with FIGURE 2.

It will be understood, that while two forms of the invention have been illustrated, many others will occur to those skilled in the art once the basic aspects of the invention are understood. For instance, rather than shunting across an electrically operated timer motor, a mechanically driven timer motor could be provided, with a movement-preventing latch being used instead of an electrical shunt. Also, a shunt may be provided in other ways from the specific way shown. For instance, a light sensitive member could be made to conduct and provide a shunt across an electrically operated timer motor without any actual electrical connection such as that provided here and the net result would be the same. Also, while I show in FIGURE 1 a preferred arrangement wherein the spaced conductors are formed as part of a rotating chamber, it is possible to make the spaced conductors as part of a stationary wall, and other ways of causing tumbling may be provided.

Thus, while in accordance with the patent statutes I have described what at present are considered to be the preferred embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications, including but not limited to those mentioned above, may be made therein without departing from the invention. It is, therefore, aimed in the appended claims to cover all such equivalent variations which fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A fabric dryer comprising:

(a) a chamber for receiving fabrics to be dried;

(b) drying means arranged to cause evaporation of moisture from the fabrics;

() means for tumbling fabrics in said chamber;

((1) spaced conductors positioned so as to be bridged by fabrics tumbling in said chamber whereby said conductors are provided with a relatively low resistance electrical bridge when there is substantial moisture in fabrics bridging said conductors;

(e) electrically operated sequence control means effective after a predetermined length of operation to terminate operation of said drying means;

(f) and a circuit providing control of said sequence control means by said conductors, said circuit including a shunt across said sequence control means, said circuit making said shunt effective whenever said conductors are provided with a relatively low resistance electrical bridge and preventing said shunt from being effective at other times.

2. The apparatus defined in claim 1 wherein said shunt includes a device which becomes conductive when a predetermined voltage is provided to it, said circuit providing said predetermined voltage whenever said conductors are provided with a relatively low resistance electrical bridge and preventing said predetermined voltage from being applied at other times.

3. The apparatus defined in claim 2 wherein said device is a silicon controlled rectifier.

4. The apparatus defined in claim 1 wherein said sequence control means includes a timer motor, and a resistance is provided in series with both said timer motor and said shunt for current limiting purposes.

5. A fabric dryer comprising:

(a) a chamber for receiving fabrics to be dried;

(b) drying means arranged to cause evaporation of moisture from the fabrics;

(c) means for tumbling fabrics in said chamber;

(d) spaced conductors positioned so as to be bridged by fabrics tumbling in said chamber whereby said conductors are provided with a relatively low resistance electrical bridge when there is substantial moisture in fabrics bridging said conductors;

(e) electrically operated sequence control means effective after a predetermined length of operation to terminate operation of said drying means;

(if) a circuit for energizing .said sequence control means including a resistor in series therewith;

(g) a shunt around said sequence control means in series with said resistor;

(h) a silicon controlled rectifier controlling completion of said shunt and having a gate, said silicon controlled rectifier becoming conductive when a predetermined voltage is impressed at said gate;

(i) and a gate circuit including said spaced conductors whereby said gate circuit causes said silicon controlled rectifier to be conductive when said conductors are provided with a relatively low resistance electrical bridge and prevents said silicon controlled rectifier from being conductive at other times, said sequence control means being precluded from operation when said silicon controlled rectifier is conductive.

6. The apparatus defined in claim 5 wherein a circuit is provided for energizing said tumbling means, and said circuit for energizing said sequence control means connected is in parallel therewith.

7. The apparatus defined in claim 5 wherein a circuit is provided for energizing said tumbling means, and an isolation transformer is provided having a primary winding in parallel with said tumbling means circuit, said sequence control means circuit being energized across the secondary winding of said transformer.

8. A fabric dryer comprising:

(a) a chamber for receiving fabrics to be dried;

(b) drying means arranged to cause evaporation of moisture from the fabrics;

(c) means for tumbling fabrics in said chamber;

(d) first, second and third groups of spaced conductors positioned so as to be bridged by fabrics tumbling in said chamber whereby said first and second groups each provide a relatively low resistance electrical bridge to said third group when there is substantial moisture in fabrics bridging said first and second groups to said third group;

(e) electrically operated sequence control means eifective after a predetermined length of operation to terminate operation of said drying means;

(f) a first energizing circuit for said sequence cona predetermined voltage is impressed at said gate means;

(i) first and second control circuits respectively connecting said first and second groups of conductors to opposite ends of said secondary winding so that direct current may pass therefrom to said third group of conductors;

(k) and a gate circuit connecting said third group of conductors to said gate means whereby said silicon controlled rectifier means becomes conductive to pre- 10 vent operation of said sequence control means when either or both of said first and second groups is provided with a relatively low resistance electrical bridge to said third group. 9. The apparatus defined in claim 8 wherein said silicon controlled rectifier means include two silicon controlled rectifiers connected in parallel with each other and conductive in opposite directions so that each provide a shunt for half of the alternating current generated in said secondary winding.

References Cited by the Examiner UNITED STATES PATENTS 2,045,381 6/1936 Elberty 34-55 X 3,200,511 8/1965 Smith 3555 X FOREIGN PATENTS 877,553 9/ 1961 Great Britain.

WILLIAM F. ODEA, Primary Examiner.

5 JOHN J. CAMBY, Assistant Examiner. 

1. A FABRIC DRYER COMPRISING: (A) A CHAMBER FOR RECEIVING FABRICS TO BE DRIED; (B) DRYING MEANS ARRANGED TO CAUSE EVAPORATION OF MOISTURE FROM THE FABRICS; (C) MEANS FOR TUMBLING FABRICS IN SAID CHAMBER; (D) SPACED CONDUCTORS POSITIONED SO AS TO BE BRIDGED BY FABRICS TUMBLING IN SAID CHAMBER WHEREBY SAID CONDUCTORS ARE PROVIDED WITH A RELATIVELY LOW RESISTANCE ELECTRICAL BRIDGE WHEN THERE IS SUBSTANTIAL MOISTURE IN FABRICS BRIDGING SAID CONDUCTORS; (E) ELECTRICALLY OPERATED SEQUENCE CONTROL MEANS EFFECTIVE AFTER A PREDETERMINED LENGTH OF OPERATION TO TERMINATE OPERATION OF SAID DRYING MEANS; 